Production of hollow metal articles



June 3, 1958 A. B. GRAHAM PRODUCTION oF HoLLow METAL ARTICLES FiledApril 22, 1955 7752/050 Paf? Unite- States PRODUCTION F HOLLOW METALARTICLES Alexander Barbour GraiiannGlasgow, Scotland, assigner to TheInternational Nickel Company, Inc., New York, N. Y., a corporation ofDelaware The present invention relates to a method for producing metalarticles containing inner passages or cavities and, more particularly,to a special method which aifords improved dimensional control in theproduction of said inner passages or cavities.

It is known that in the manufacture of special metal shapes, such as gasturbine blades or guide vanes ernployed in aircraft gas turbines, it isfrequently desirable to provide inner passages or cavities in suchblades or vanes. Thus, the gas turbine designer may wish to provideinternal cooling for the blades and/ or vanes used in the hot zone of agas turbine and in such a case passages must be provided in the blades,etc., to carry the coolant, which is usually a gas. Again, it may bedesired to reduce the weight of the rotating gas turbine members andthis may be accomplished by hollowing out the blades, e. g., byproviding internal passages therein.

Those skilled in the art know that the blades or vanes which areemployed in the high temperature portions of a gas turbine are made ofVery refractory high temperature alloys, such as nickel-chromium alloys,nickel-chromium-iron alloys, nickel-chromium-cobalt alloys, etc. Thesealloys also may contain substantial amounts of other alloying oraddition metals, including tungsten, Vanadium, molybdenum, aluminum,titanium, columbium, etc. Because of the refractory nature of suchalloys, it is a practical impossibility to drill the finished parts madetherefrom, e. g., a gas turbine blade or vane, to provide internalpassages or cavities therein, especially when such passages or cavitiesare of small diameter.

Accordingly, it has been proposed heretofore to provide inner passagesor cavities in such articles by a process comprising drilling a metallicbody or billet which is made of an appropriate metal for the desiredservice, lling the resulting holes with a filler material and then hotworking the resulting metallic body by extrusion or otherwise. Theresulting hot worked article can then be cut to desired size and theiller material can be removed to provide the desired inner passages orcavities therein. Usually, the passages or cavities extendlongitudinally through the worked article.

It. has been found in practice that the hot working characteristics ofthe ller material, in relation to the hot Working characteristics of thebillet metal, govern to a great extent the uniformity of dimension inthe elongated holes resulting from the hot working of the initiallyfilled billet. Thus, if the iiller material is more readily deformablethan the metal, the reduction in the cross-sectional area of the filledhole during hot working will be proportionately greater than that of themetal.

In addition, the said cross-sectional area will vary alongv the lengthof the hole. On the other hand, if the iller is less readily deformablethan the metal, it will act as a mandrel in the extrusion. In thismanner, the filler will pass through the die before extrusion of themetal is complete and the trailing end of the extruded section willarent icc contain no filler. In addition, the cross-sectional area ofthe hole formed will be irregular.

I have now discovered a method whereby the dimensional accuracy ofinternal passages or cavities produced during the hot working of billetscontaining filled holes can be achieved with a high degree of controlover the dimensions of the final passages or cavities produced in thehot worked article.

It is an object of the present invention to provide a method whereinimproved dimensional control is achieved in the production of hot workedmetal articles containing internal passages or cavities.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawings inwhich:

Fig. l is a sectional view of a billet illustrating a blind cored holedefining a concentric core of billet metal;

Fig. 1A depicts the cored hole of Fig. l iilled with iiller material;

`Fig. 2 is illustrative of the billet in Fig. 1A in an extrusion press;

Fig. 2A depicts the extruded billet;

Fig. 2B shows the extruded billet with core and filler removed; and

Fig. 3 is illustrative of another embodiment carrying out the presentinvention.

According to this invention, the hole or each hole initially produced inthe billet is of annular or other section such that a core is leftinside it. Preferably, the holes are machined or cut by electric erosioninto the billet or the like. It is also preferred that the erosion bestopped before the hole passes right through the billet or the like sothat a closed end is left. A dissimilar filler is then inserted in eachhole around the core, i. e., the space be tween each core and eachcorresponding wall in the billet is filled with the iiller material,andthe billet or the like is worked to the desired cross section.Thereafter, the closed end is removed. After the filler has beenremoved, by acid leaching or otherwise, the core in each hole is looseand can also be removed. Alternatively,

the original hole can be made right through the billet orl the like sothat the core is freed, and this free core (or a like core ofessentially the same composition) is used inside a filler to iill thehole before the billet or the like is worked.

The process of electric erosion is described, for instance, in AircraftProduction dated August 1952, pages 271 to 274.

The method according to the invention presents the advantages that theholes can be of any desired cross section, whereas only circular holescanl be made by drilling and that, by the use of electric erosion,annular or other-sectioned cored holes of very small width can be madeso that the total volume of ller required to ll them is small, with theresult that the time taken to remove the iiller subsequently is muchreduced.

The removable ller should have the same deformation characteristics asthe metal of the billet or other blank. It may advantageously be used asa preformed metal sleeve inserted into the hole varound the core. Itshould, of course, be attacked by a leaching acid more easily than themetal of the blank or be otherwise capable of removal without damagingthe blank. Thus, the filler material should, for example, be susceptibletoa selective chemical or electrochemical attack as compared to thebillet metal.

When the removable filler is a preformed sleeve, e. g., is a section cutfrom a length of extruded or cold drawn metal, it or a duplicate (e. g.,another section `cut from the same extruded or cold drawn length) may,when the filler material is' suitable, be used with advantage as theracy Yand 'control in the production of the desirefd paselectrode in theerosion process. It will be seen in accordance with the foregoing thatVthe hole or holes which are machined into the initial billet have innerand outerwalls de'ningia-substantially concentric coreandfniayiconvenientlybe referred lto as .cored holes which Ymay have anycros's-sectionalfconfiguration. Vit Visfpreferred in accordance with theinvention to discontinue the drilling operationbeforeV the core becomescompletely detached from-the remainder of the billet, i. e., it ispreferred jto drill'a .blind cored hole. In this way, the core remainsfastened in its place in the billet and the lling of the cored h'olewiththe desired filler material-is facilitated.

The required iiller material may bef-selected from a number of suitablematerials. depending'to some extent Y upon the ,nature of the particularheat-resisting alloy being worked. Y As an'eXample, itcan be Apointedout that the iron-magnesia ller materialdisclosed Vin the Hignett U. S.application Serial No. 472,755, tiled December 2, Y

1954, may beY employed satisfactorily in accordance with this inventionin the treatment of many of the common heat-resisting alloys used inmanufacturing gas turbine blades and vanes. VAnother satisfactory llermaterial comprises a special `alloy steel containing about 1% to Ytitanium, about 5% to 20% Vmanganese and up to about 0.5% carbon and isthe subjectl matter of Va separate patent application Serial No. 509,380in the name of Walter'Betteridge.

yFor the purpose 0f giving those skilled inthe art abetter'unders'tanding Yof the invention, reference is now made to thedrawing illustrating, by way of example,

procedural steps by which the presentinvention can be carried intopractice. Y Y

Referring to Fig. l, there isillustrated a cylindrical billet10 in whichcored hole 12 has been provided, e. g., by electric erosion or other`machining processes. The hole which is illustrated as ofannular crosssection can be of other suitable cross section. As referred tohereinbefore and as shown in Figs. 1 and 1A, itis desirable todiscontinue the machining operation short of oneV endY of the billet tothereby provide a blind cored hole having a substantially concentricintegral coreV 14 of billet metal. A suitable filler material V16 llsthe cored hole 12 and the billet can be then hot worked, e. g., byan-extrusion operation. The ller material can be in compacted powderform or desirably in the form of metal sleeves, or in other 4suitableforms apparent to those skilled in the art. As shown in Fig. 2, the ram18 forces the cored billet Vthrough die orifice 20 to thereby provide anextrudedY product of predetermined configuration such as illustrated inFig. 2A. The extruded product can be then Vcut and the ller materialremoved therefrom .by leaching or otherwise.V The coreyis easily removedyas shown in Fig. 2B.

In Fig. 3, there is depicted a modiiication for providing acored hole ina billet and filling the same with a filler material. In this instance,a preformed metallic sleeve 22 is employed as the electrode or drilltube in the machining process,'e. g., electric erosion. The sleeve afterthis operation then serves as the ller material. As will be readilyunderstood by those skilled in the art, a suitable arc Vlength ismaintained and a suitable coolant can be employed during the erodingoperation.

vIt will be seen that when the lled billetproduced in accordance withthe present invention is hot worked as by extrusion or hot rolling, thecore and the filler in the hole ow in a similar way to the remainder ofthe billet.

n This factor contributes to improved dimensional accusages and/orcavities in the final hollowmetal article.

Although the present` invention has been described in conjunction withpreferred embodiments, itis to be understood that modifications andvariations may be resorted to without departing fromthe ,spirit andscope of the invention, as those skilledin the art willreadilyunderstand. Such modifications and variations are considered tobe within the purview and scope of the invention and appended claims.

IclaimiV Y A l. The method for producing Ya hollow metal having at leastone internal passage or cavity comprising electrically erodingl a metalbillet to provide therein at least one longitudinally located, annular,blind hol'e having inner and outer walls dening'a substantiallyconcentric, integral core of billet metal, V'said electric erosionmetal'electrode sleeve; leavingVsaidpelectrodeisleeve in Y' and saidfiller mz-,lterialy to Valterrthe cross. section thereof,

situ to thereby ,provideV `a ller material in `said cored hole; hotworking the resulting billet in a `direction parallel to said filled,Ycored rhole to changethe Ycross section of said billet and, said coredhole; and removingnthe'ftller material and corefrom each holeV toprovidea worked Y metal articleV hav-ing'atlleast one passageV orcavitytherein.

V2. The methodifor producing Yauliollovv metal article which comprises4electrically eroding 4a `metal billet to f provide therein at leastoneblind hole having inner and Y outer walls denning ai substantiallyconcentric, kintegral y core of billet metal,saidelectricerosionoperation being Y performedwhile utilizing 'yapreformedelectrodesleeve;Y f leaving saidrelectrode Vsleeyefin sitntorpthe'reby provide 'j aY iiller material in said cored hole;workingthe, resulting billet to change the cross sectionthereofandjremov- K ing the sleeve and core from said hole totherebyprovide a hollow metal article havingr` at Yleast one Vpassage Aorcavity therein. j

ELAV method-for producing Va. hollowme'tal. article 1 Y' characterizedbyV atleast one internal passagefof uniformV cross-sectionall area'along the'Y length thereof v'which CnlV v prises providing inriarmetalbillet of refractory/*high Vteinperature alloy Yat least oneannular blind holegfsaid alinularhole having an` inner VVWallconstituting the outer` surfaceof a self-sustainingunremoved andsubstantially concentricY core ofvrbnilletY metal integral with-saidbillet,A

filling the space between ,theV self-sustaining integrali'e of billetmetal and the outer WallV of said blind .hole with adissimilar'iillermaterial having substantially thesaine deformationcharacteristics as .the metal of the billet,

working the resulting vbillet having said blind-hole cn-L taining vsaidself-sustaining integral Vcore f; billet metal cropping the` end wherethecore is wintegral" with the billet to separate theV core from theconnecting body ofY the formed billet, selectively removingtthe fillermaterial,

and then removing the core. K l

- References VCited inthe Viile of .thisr'patent UNrTED STATES PArEN'rs1952, pages 92 and93. y

article

1. THE METHOD FOR PRODUCING A HOLLOW METAL ARTICLE HAVING AT LEAST ONEINTERNAL PASSAGE OR CAVITY COMPRISING ELECTRICALLY ERODING A METALBILLET TO PROVIDE THEREIN AT LEAST ONE LONGITUDINALLY LOCATED, ANNULAR,BLIND HOLE HAVING INNER AND OUTER WALLS DEFINING A SUBSTANTIALLYCONCENTRIC, INTEGRAL CORE OF BILLET METAL, SAID ELECTRIC EROSIONOPERATION BEING PERFORMED WHILE UTILIZING A PERFORMED METAL ELECTRODESLEEVE; LEAVING SAID ELECTRODE SLEEVE IN SITU TO THEREBY PROVIDE AFILLER MATERIAL IN SAID CORED HOLE; HOT WORKING THE RESULTING BILLET INA DIRECTION PARALLEL TO SAID FILLED, CORED HOLE TO CHANGE THE CROSSSECTION OF SAID BILLET AND SAID CORED HOLE; AND REMOVING THE FILLERMATERIAL AND CORE FROM EACH HOLE TO PROVIDE A WORKED METAL ARTICLEHAVING AT LEAST ONE PASSAGE OR CAVITY THEREIN.